The subject matter described herein generally relates to a system and method for time-domain simulation. More specifically, an embodiment relates to time-domain computation of scattering spectra (e.g., electromagnetic (EM) spectra) for use in spectroscopic metrology.
Time-domain simulation has been used to compute scattering properties. Typically, a scattering geometry is given from which transmission and reflection coefficients are computed, as well as their associated phases.
Typical optical systems have a finite spatial width for the apertures used to produce the light incident on the scatterer, and define the range of collection angles. In order to accurately model the scattering process, it may be necessary to model the finite spread of incident angles.
The problem has traditionally been solved in the time-domain by performing the scattering computation for a fixed set of angles that samples the finite angular spread of the aperture. The reflection and transmission spectra are then computed as a weighted average of the spectra of the spectra obtained at each incident angle. Unfortunately, the computational load grows linearly with the number of angle samples used. Hence, for high accuracy work, e.g., required in scatterometry, 3 to 9 incident angles may be used, resulting in a factor of 3 to 9 increase in the computational time.